Comparison of C collected by precipitation and gas-strip methods for dating groundwater

Nakata, Kotaro*; Hasegawa, Takuma*; Iwatsuki, Teruki  ; Kato, Toshihiro

Dissolved inorganic carbon (DIC) for C analysis of groundwater is usually extracted by a gas-strip or precipitation method. In this study, the certainty of the two methods for C dating were confirmed. DIC and C concentrations obtained by the gas-strip method were close to the theoretically predicted C value. Conversely, the C value obtained by the precipitation method always showed higher values than the predicted values. The difference in C value between gas-strip and precipitation methods was assumed to arise owing to contamination of modern carbon used in the precipitation method. The applicability of the precipitation method for groundwater should be considered carefully according to the DIC, C concentration of groundwater and purpose of the study being conducted.